Process for the manufacture of boric acid



Jan. 4, 1938. W.,E. BURKE ET AL 2,104,009

PROCESS FOR THE MANUFACTURE OF BORIC ACID Filed June 25; 1929 HOTCONCEHTRA Ten SOLUTION "A" (Bonn): AND SULPHU'PIC Acm) COOL.

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CEHTRIFUGE GLAuBeRs SRLT N THE L U01? NR2 sofiElgfizo 0 up" Q A171]SULPHURm flcmmmBoRnx fzz'ventor HEHT (14s HBOVE) Patented Jan. 4, 1938mater PROCESS FOR. THE MANUFACTURE OF BORIG ACID William E. Burke, am,cans, and Harald de Ropp, Charleston, W. Va., assignors to AmericanPotash & Chemical CorporatiomTrona,

Califi, a corporation of Delaware Application June 25, 1929, Serial No.373,639 A ieoiaim's. 7 (01. 23-449) The invention relatesto'improvements in the manufacture or" boric' acid-from certain metalborates. In particular this invention relates to an economicaland'efficient cyclical process for 5 producing boric acid from suchmetal borates as produce upon reaction with sulphtu ic acid a solublesulphate and boric acid. The invention includes improvements in acyclical process and in cer'tainnovel steps thereof. g V

When bcrax, the most common metal borate is treated with sulphuric acid,the reaction prodnets are boric acid, sodium sulphate and Water, asillustrated by the following type equation:

The process of the present invention is hereafter described in terms ofsodium tetraborate,

for the reason that this material occurs most abundantly in nature andis wellsuited to the herein described process. However, any suitablemetal borate such as Ulexite, Razorite and Boracite, or mixtures of tWoor more borates, capable of fulfilling the conditions specified'withinthis invention maybe employed.

,Referring to the preceding reaction equation, if just sufficient wateris present to keep the sodium sulphate'in solution, a considerable partof. the resulting boric acid may be recove'redas a crystallinerecipitate, for example, by cooling, due to thelow' solubility of theboric acid as compared with that of the sodiumsulphate, However, theboric acid which remains in solution constitutes a serious loss if theremaining solution is discarded. Attempts to recycle theremainingsolution through theoperation, in order to secure more complete recoveryof boric acid, have encountered several difiiculties; for example, waterformed in thereaction progressively increases tlie. volume of thecirculating solution, and the progressive increase in the amount, ofsodium sulphate present results in contamination of the boric acidproduced with sodium sulphate.

This application is a continuation in part of cope-riding applicationSerial No. 207,614. filed July 22, 1927.

it is the general object of the present inven tion to provide a processin which sodiumsulp teinay be recovered from the solution to beecirculated whereby the progressive increasein .he amount of sodiumsulphate present in the solution is avoided and a pure boric acidproduced, while at the same time the boric acid content of a thesolutionremaining after precipitationfof the V boric acid therefrom isrecovered. V.

The present invention comprehends that a solution containing sodiumpentaborate, that is, a mixture of borax and boric acid, will hold moreboric acid or boron than either asolution-of borax or boric acid at thesame temperature. 5; Accordingly, after the solution of boric acid,produced from the reaction between borax and sulphuric acid, is cooledto precipitate boric acid and brought nearly to the saturation pointwith respect to the sodium sulphate present, part of l; the sodiumsulphate content may be precipitated from the solution without furtherprecipitation of boric acid or boron compoundspprovided a portion of theboric acid of the solution is first converted to the pentaborate. Whenthe boric 1 acid of such a-solution is neutralized and converted intomore alkaline compounds, such as the pentaborate and thetetraborate,-the solu tion is no longer saturated'with' respect to" theboric acid originally present and may be'cooled k with; resultantprecipitation of sodium sulphate without loss of the valuable boroncontent.

The solubility of boron compounds in'solution increasesso markedly asthe boric acid is'converted in part to the pentaborate or further to amixture of the pentaborate and the tetraborate that the solution'may berendered unsaturated with respect to the boric acid originally presentby adding such metal boron compounds as are capable of causingneutralizationiof the boric 5w acid. Thus a solutionsaturated withrespect to boric acid is rendered unsaturated by addingv thereto anysuitable metal'borate. Any sodium boron compound'containing more sodiumcontent, than the pentaborate may be added for this pur- 35 pose, i. e.,borax or sodium metaborate'may be employed as conditions warrant.

" It has: also been found economical under certain 'circumstances toemploy alkalis or alkali salts; which contain no boron, for the purpose40 of neutralization. Anyof thecommon reagents capable ofproviding'suflicient hydroxyl ions for the neutralization'or partialneutralization of the boric acid-may be used provided that theyintroduce no. permanent undesirable materials into 45 r the solution. Ofthe latter class of compounds,

are the carbonates, the oxides and hydroxide oi sodium;'Ifhepentaborateis forr'ned'from these 1 different materialsinaccordance with the following reactions: t (1)61-13303+Na2B4O7=Na2B1nO1s+9H2O (2) 8H3BO3-1-N'L2B2O4:NazBmOm+12H2O (3)IOHsBOs+Na2CO3=Na2B10O1s+15I-I2O+CO2 As will be apparent from aninspection of Equation (1), where borax is used to form the pentaborate40% of the boron content results from the borax added. In the case ofEquations (2), (3 and (4), where sodium metaborate, sodium carbonate,and sodium hydroxide are employed, the boron in solutions of Equation(2) is only 20% derived from the metaborate, while all boron in thesolutions of Equations (3) and (4). is derived entirely from boric acid.

Whether metal boron compounds or other suitable compounds such as freealkali, as above described, are employed for the partial neutralizationof boric acid prior to the removal of the soluble sulphate dependslargely upon economic considerations. The yield of boric acid per cycleof the present process is dependent upon the quantity of sodium sulphatewhich may be removed subsequent to the precipitation of the essentiallypure boric acid. The quantity of sulphate removed is dependent upon thetemperature to which the liquor may be cooled for its precipitation,without causing simultaneous precipitation of valuable boron compounds.By the use of suitable boron-free neutralizing agents in the step ofpartial neutralization of boric acid, the resulting solution containsless boron, hence lower cooling temperatures may be tolerated, with aresulting larger yield per cycle of boric acid than whenboron-containing neutralizing agents are employed. Hence in localitieswhere alkalis, e. g., NaOH and NazCOa are cheap it may be advisable toemploy these in place of borax.

A larger yield per cycle is obtained, thereby de creasing productioncosts from the standpoint of efficiency of time, labor and equipmentrequirements, etc. offsetting such advantages are the disadvantages ofthe cost of the boron-free alkali employed and the acid required for itssubsequent neutralization.

In localities where such materials are relatively expensive it may beadvisable to employ boron-containing alkalis, e. g. borax or sodiummetaborate, with a resulting lesser yield per cycle.

The complete process of the present invention comprises the followingsuccessive steps: 1, treating a solution including sodium tetraboratewith sulphuric acid to form boric acid and sodium sulphate; 2,separating boric acid from the resulting solution; 3, neutralizing aportion of the residual boric acid, after separation of boric acid; and4, separating sodium sulphate and water from the resulting solution;with return of the solution remaining after separation of sodiumsulphate to the first step.

The invention thus provides an improved cyclic process which includesthe removal of water and sodium sulphate formed in the operationenabling t the maintenance of uniform operating conditions in the cycle.The invention also provides for substantially complete recovery of theboric acid free from contamination with sodium sulphate.

In carrying out the present invention, under such conditions that theuse of borax (Na2B407. 1OH20) is preferred, a solution containing.sodium tetrasulphate, in the form of dekahydrate, and boric acid areprecipitated together.

In carrying out this invention, however, sodium tetraborate is added tothe solution before separation of sodium sulphate. The solution, Withadded sodium tetraborate, is then further cooled with consequentcrystallization of sodium sulphate, and this crystallized sodiumsulphate is then separated from the solution, for example, in acentrifuge. The increase in the solubility of boric acid effected by theaddition of sodium tetraborate makes it possible to remove sodiumsulphate in this manner without loss of boric acid. This further coolingis carried to a temperature slightly higher than that at which fur therseparation of boric acid from the solution begins.

In the cyclic operation of the invention, an amount of sodium sulphatecorresponding to that formed is removed in this manner in each cycle.This removal of sodium sulphate as the dekahydrate consequently effectsthe removal from the circulating solution of an amount of water twicethat formed by the reaction between the sulphuric acid and sodiumtetrahorate dekahydratc. It is advantageous to add water to thecirculating solution, to maintain its volume, after the separation ofboric acid and'before further cooling of the solution for separation ofsodium sulphate. This further assists in preventing loss of boric acidand permits 'a more effective separation of sodium sulphate.

The solution remaining after separation of sodium sulphate, in carryingout the invention. contains residual sodium sulphate and boric acid andis returned to the first step of the operation in which, together withadded sodium tetraborate, it is subjected to treatment with sulphuricacid and the operation repeated.

While the improved cyclic process of the invention can be carried outover a Wide range of temperature and concentration conditions, the

example .of operation given below represents a particularly advantageousone. In any case, the operation is advantageously carried out so thatthe boric acid and sodium sulphate formed in each cycle are completelyseparated in the same cycle. Increase in the quantity of boric acidproduced in the reaction between sulphuric acid and sodium tetraborate,per cycle, also involves a corresponding increase in the production ofsodium sulphate, and this limits the temperature to which the resultingsolution can be cooled before contamination of the crystallized boricacid with sodium sulphate begins. As the temperature to which thesolution is cooled rises, an increasing amount of boric acid remains inthe solution so that further cooling for separation of sodium sulphateis in turn limited by the increased tendency of boric acid to separatewith the sodium sulphate in this subsequent op eration. The operation isthus advantageously carried out under conditions such that the maximumamount of sodium sulphate is separated, per cycle, without loss of boricacid with the so dium sulphate.

The best yield per cycle of boric acid free from contamination withsodium sulphate is obtained whenthe initial cooling for separation ofboric acid is carried to the lowest temperature pos sible before theseparation ofsodium sulphate begins and when further cooling of theremaining solution after the addition of sodium tetra-- diumsulphateandto prevent loss of boric acid;

A temperature margin of say 1.5 C. may be 2.1-.

lowed, for example, but'fthis maybe increased or decreased as theoperating conditions warrant "with accompanying decrease or increase inthe 'yield per cycle. c l 'The follbwing example will further illustrateaccompanying. drawing, in" which The figure'is a flow sheetofthe-process;

the invention, the description referring to the The solutionF'recycledfflfrom ,-a previous operation, contained about '10 .l'lbs.oiboric'acid, 2 1bs. of sodium tetraborate, 33.3 lbs. of sodiumsulphatefand 100 lbs. off-water; was at a temperature of aboat"24.2- C.To'this solution about 17.4 lbs. of sodiurntetraborate delahydrateand"5.4 l lbs." of 100% sulphuric The-resulting solution (A) containedabout 2319 lbs. of boric acid, 412 lbs. ofsddium's'ulphate and 103.2lbs; of water; 'This solution was cooled to about 2'7.'7 C. and about13.8 lbs. of crystallized boric acidseparated. The remaining solution(C) contained about 10.1 lbs. of boric acid, 41.2 lbs. ofsodium-sulphate and 103.2 lbs. of water; To this solutionwere addedabout 3.8 lbs. of sodium tetraborate dekahydrate and 5' lbs. of water.The resultings'olution (D) contained about 10.1 lbs. of boric acid, 2.0lbs. of sodiumtetraborate, 41.2 'lbs.- of

sodium" sulphate and 110- lbs; of water. This solution' was cooled toabou't 24.2 C.'and about 17.9 lbsiof' crystallized sodium sulphatedekahydrate separated. *The'remaining solution contained about 10.1 lbs.of boric.acid, 2 .0 lbs. of sodium tetrabora'te, 33.3 lbs. ofjsodiunrsulphate 1 and 100 lbs. of water. The operation was then repeated withthis solution. i a

The foregoing illustrative, example represents an" operation carriedoutwith pure materials, NazBgOilOI-IgO'ahd nzsolq Itfwill be understoodthat different borate materials :and various impurities may makedifferent changes in the operation desirable. L

' In "any event, however, the solution resulting from treatment of themetal borate with sulphuric acid is 'best cooled as far aspossiblebefore the separation of the s'olublesulphate begins; and the'remainingsolution after separationof crystallized boric acid and partialneutraliz'ationof the residual boric-acidis best further cooled as faras possible before further separationof boric acid begins.v

As pointed outabove, it IS advantageous-to separateas much' sodiumsulphate as possible, per cycle, without loss of boric acid. To thisend, it is advantageous, to supply'to' the treatment with sulphuric acida dehydrated or partially dehydrated borax, that is sodium tetraboratewith less Water of crystallization than correspondsto'the dekahydrate.By' supplying dehydrated or partiallyndehydrated borax to the sulphuricacid treatment, the

' This solution;

' withil an evaporating operation.

volumeof the resulting solution (A) may be reduced with consequentincrease in the proper-'- tionoiboric acid precipitated on cooling thissolution. With the separation of an increased proportion of the boricacid, an increased amount of water may be added'to the solution beforeseparation of sodium sulphate tomaintain its volume, and due to thereduced amount of boric acid in the resulting'solution it may then becooled to a lower temperature before the separation of boric acid-againbegins, making pos-' sible the separation of an increased amount ofsodiumv sulphate.

amounts of sodium tetraborate and sulphuric acid inleach cycle withconsequent increase in v In this manner, the amount of sodium sulphatein the recycled solution may be reduced, making it possible to useincreased p I the yield per cycle of boric acid whilenevertheless'maintaining uniform operating conditions boratetetrahydrata'or totally dehydrated sodium tetraborate in the process.borate pentahydrate may be produced, for ex- "ample, by crystallizationabove the transition point from-hot concentrated borax solutions. Sodiumtetraboratefltetrahydrate occurs in certain-natural deposits and may bep-roducedby crystallization under suitable conditions of elevated'temperature and pressure By the use'of sodium tetraborate pentahydrate,the yield per cycle of boric acid may be increased. as much as 28%, ascompared to the yield per cycle using 1 sodium tetraborate dekahydrate,ordinary borax. The use of totally dehydratedsodium tetraborate Sodiumtetramakes it possible'toincrease the yield per cycle of boric acid asmuch-as 57%.

,Referring to the sodium tetraborate added to the solution remainingafter initial cooling and separation of boric acid, it is unimportantwhether borax or dehydrated or partially dehydrated borax-is used sincewater is added tothe solution circulating in the cycle at this. point inthe operation. In case that totally dehydrated borax isemployed in thesulphuric acid treatment, it becomes necessary to add slightly more, say10% more borax, to the solution C for the preparation of solution D,than in the case where dekahydrate borax. is employed.

. A" similar improvement in the operation may. be obtained byevaporation of water from the solution recycled in the process, eitherbefore or' after-the further addition of sodium tetraborate andsulphuric acid. The'solution A containing added sodium tetraborateandsulphuric acid" is ordinarily. heated to promote the reaction, andthis operation may be conveniently combined Or, cooling of the solutionA resulting from the treatment of sodium tetraborate with sulphuric acidmay be promoted or in part effected by evaporation under subatmosphericpressure.

,In this way, an increase in concentration of thesolution from whichboric acid is separated, with improved results similar to those wherethis water is eliminated by using dehydrated or partially dehydratedborax is obtained. Such removal of water by evaporation also makes itpossible to carry this concentration further than is possible simply byeliminating water of crystallization fromv the sodium tetraboratesupplied to the operation. 1 r

nomic conditions that the use of free alkali as a neutralizing agent ispreferable, the process as hereinbefore set forth by example may becarried out in an entirely similar fashion. The following example willillustrate the operation of the process of this invention whereinpartial neutralization is brought about by the addition of caustic soda.

While this feature may be employed in any one of a number of thepossible variations of the present process, the following example ischosen as nearly parallel to the one preceding as possible, in order toshow, most clearly, the valuable increase in yield per cycle which maybe obtained by such procedure;

The solution, F, recycled from a previous operation contained about 9.0lbs. of boric acid, 1.8 lbs. of sodium tetraborate, 27.8 lbs. of sodiumsulphate and 100 lbs. of water. This solution was at a temperature ofabout 223 C. To this solution about 46.7 lbs. of sodium tetraboratedekahydrate and 12.9 lbs. of 100% sulphuric acid were added. Theresulting solution A, contained about 41.5 lbs. of boric acid, 46.4 lbs.of sodium sulphate and 110.2 lbs. of water. This solution was cooled toabout 285 C. and about 30.3 lbs. of crystallized boric acid separated bymeans of a centrifugal machine. The remaining solution, C, containedabout 11.2 lbs. of boric acid, 46.4 lbs. of sodium sulphate and 110.2lbs. of water. To this solution were added about 0.71 lb. of 100%equivalent sodium hydroxid dissolved in 12.3 lbs. of water. Theresulting solution D, contained about 9.0 lbs. of boric acid, 1.8 lbs.of sodium tetraborate, 46.4 lbs. of sodium sulphate and 123.6 lbs. ofwater. This solution was cooled to about 223 C. and about 42.3 lbs. ofcrystallized sodium sulphate dekahydrated, (Glauber salt), separated.The'remaining solution contained about 9.0 lbs. of boric acid, 1.8 lbs.of sodium tetraborate, 27.8 lbs. of sodium sulphate and 100.0 lbs. ofwater. The operation was repeated with this solution.

The preceding example clearly shows that more than twice as much boricacid may be produced per cycle by the use of free alkali as comparedwith the identical process employing borax for partial neutralization ofthe boric acid, prior to cooling for the removal of the hydratedsulphate. The temperature factors of safety, i. e., the temperaturedifference between the point of saturation and the point of cooling,were even greater in the latter case than in the former.

Whatever be the nature of the neutralizing agent employed is of littleconsequence to the scope of the present invention; the selection beingentirely one of economic consideration. The addition of any reagentsuited to the purpose of partially neutralizing the boric acid prior toseparation of the soluble sulphate is an important part of the presentinvention providing an improved cyclical process as herein set forth.Particularly, greater amounts of caustic may be used than in theforegoing examples, and the solution may be brought to saturation withpentaborate and borax rather than saturation with pentaborate and boricacid.

As the yield per cycle is increased the solubility limits of both theraw material, borate, and the product, boric acid, are approached. It isdesirable to have all the borate in solution prior to the precipitationof boric acid, in order to prevent contamination of the product, boricacid, with unreacted borate. Also in many cases it is desirable tofilter the. solution prior to the, precipitation of boric acid.

The borate employed often contains undesirable foreign matter. To filtersuch material therefrom it is necessary that the borate be entirely insolution. In certain cases in the past, the factor limiting the quantityof boric acid that might be produced depended upon the quantity of boricacid which might be held in solution at the temperature most suited tofiltering operations.

However, by the process of this invention this limiting factor has beenovercome. This invention comprehends that a solution containingpentaborate, that is a mixture of borax and boric acid will contain amuch greater quantity of boron than either a solution of borax or boricacid at the same temperature. Hence it is preferred that the reactionsolution, A, be prepared by adding thereto the desired quantity of boraxor other suitable borate, together with approximately of the total acidrequired. Theresulting solution containing a mixture of boric acid andborax easily contains the total boron of the system in solution at arelatively low temperature.

Consequently the resulting solution may easily be filtered for removalof extraneous solid matter. The remaining acid is then added prior tothe cooling operation for the removal of boric acid. It is not necessarythat the whole of the boric acid crop produced by the addition of theremaining acid be soluble at the temperature of the reaction. Since theborate material is completely dissolved by this novel process, danger :1

of occlusions thereof with the precipitating boric acid is eliminated.Obviously this feature of the present invention is of great value in theeconomical and efiicient manufacture of boric acid from suitable boratematerials.

In addition to the aforementioned advantages, the production of thepentoborate liquor during the operation of preparing the reactionsolution A, is further efiicient. Where cooling is carried out in coilcoolers, i. e. by means of indirect heat transfer, a coating of boricacid is deposited upon said coils, or their equivalent. This deposit isdfficult of solution. In the past it has been the practice to removesuch deposits by means of hot water, thereby entailing a loss ofvaluable boric acid. The strong pentaborate liquor of the presentinvention has been found to have a remarkable affinity for such depositsof boric acid; the rate of solution of the deposited material in thehot, semi-complete reaction liquor containing a large amount ofpentaborate being very considerably greater than in the hot waterpreviously employed. Beside the advantage of time and ease of operationgained thereby, the valuable boric acid is caused to remain within thesystem and may be recovered. with the boric acid produced in the cycle,upon subsequent cooling. The advantages as shown above may be combined,that is, the hot strong pentaborate liquor may be first utilized for thedissolution of deposited boric acid, then passed through a filter forthe removal of foreign matter, or vice versa. Hence, this feature of thepresent invention i of great practical value.

Throughout the preceding description of the novel and valuable processof this invention the examples and. exposition have been largely givenin terms of common borax. It must be understood that the other boratematerials are also of value. to the process, providing such boratestreatment with sulphuric acid.

yield in whole or in part asoluble sulphate upon For instance, thebimetal borate Illexiteior Cotton Ball may be advantageously employed.Ulexite is a'double borate of calcium and sodium. Uponappropriate-treatment with sulphuric acid, sodium sulphatecalciumsulphate andboric acid are formed. The calcium sulphate so formed beinginsoluble may be removed by filtration orv other suitable means and theremaining solution subjected-to the process of the presentjinvention ashereinbefore described. a 1

.While the acidification of 'borax has been shown in terms ofapproximately equivalent quantities of sulphuric acidit: is preferredthat a slight excess of sulphuric acid be present in the reactionsolution A, prior to cooling f for precipitation of boric acid. Theadvantage. of this slightexcess of strong acid resides in its ability towithhold in solution certain undesir able impurities, such as iron,etc., thereby insur ing a boric acid product of satisfactory color.

While the particular processes herein described are well adapted tocarry out the objects of the present invention, it is understood thatvarious modifications and changes may be made withtion of boric acid,partially crystallizing out sodium sulphate from" the resultingsolution, andfreturning solution remainingafter separation 0 sodiumsulphate to the first treatment 2. .An improved cyclic process of Imanufacturing boric acid and'sodium sulphate, comprising successivelytreating ;a solution including sodium tetraborate with sulphuric acid toform: boric acid and sodium sulphate, partially crystallizing out boricacid from the resulting solution, adding sodiuml tetraborate and Waterto the solution after separation of boric acid, partially crystallizingout sodium sulphate from the resulting solution, and returning solutionremaining after separation of sodium sulphate to the first treatment.

3. An improved cyclic process of manufacturing boric acid and sodiumsulphate, comprising successively treating a solution including sodiumtetraborate with. sulphuric acid to form boric acid and sodium sulphate,separating water from the solution treated with sulphuric acid,partially crystallizing out boric acid from the resulting solution,adding sodium tetraborate to the solution aft-er separation of boricacid, partially crystallizing out sodium sulphate from the resultingsolution, returning solution remaining after separation of sodiumsulphate to the first treatment.

4. An improved cyclic process of manufacturing boric acid and sodiumsulphate, comprising successively treating a solution in which has beendissolved sodium tetraborate containing less than ten molecules of waterof crystallization per molecule of tetraborate with sulphuric acid toform boric acid and sodium sulphate,f partially crystallizing out boricacid from the resulting solution,

adding sodium tetraborate to the solution after the separation of boricacid, partially crystallizing .out sodium sulphate from. the resultingsolution, and returning solution remaining after separation of sodiumsulphate to the first treatment.

5. An improved cyclic process of manufacturing boric acid and sodiumsulphate, comprising suc-;

cessively treating a solution including sodium tetraborate withsulphuric acid to form boric acid and sodium sulphate, partiallycrystallizing out boric acid from the resulting solution, adding sodiumtetraborate to the solution after separa tion of boric acid, partiallycrystallizing out sodiumsulphate from the resulting solution,returning'solution remaining after separation of sodium.

sulphate to the first treatment, maintaining the watercontent of thesolution prior to crystallization of boric acid as low as possible whileinsuring completion of reaction and increasing the water content afterpassage of boricacid to the point where the remaining boric acid willremain in the solution during crystallization of the sodium sulphate. I

6. An improved cyclic processof manufacturing boric acid and sodiumsulphate, comprising treating a solution including sodium tetraborate awith sulphuric acid to form boric acid and sodium sulphate, cooling theresulting solution to a temperature just above that at which thecrystallization ofsodium sulphate begins and separating the crystallizedboric acid, adding sodium tetraborate to the solution after separationof boric acid,

cooling the resulting solution to a temperature just short of that atwhich separation of boric acid again begins and separating thecrystallized sodium sulphate, and returning solution rema'ining afterseparation of sodium sulphate to. the first treatment.

7. An improved cyclic process of manufacturing boric acid and sodiumsulphate, comprising treat-' ing-a solution including sodium tetraboratewith sulphuric acid to form'boric acid and sodium sulphate, cooling theresulting solution to a temperature just above that at which thecrystallization of sodium sulphate begins and separating thecrystallized boric acid, adding. sodium tetraborate and water to thesolution after separation of boric acid, cooling the resulting solutionto a temperature just short ofthat at which separation of boric acidagain begins and separating the crystallized sodium, sulphate, andreturning solution remaining after separation of sodium sulphate tofirst treatment.

8. In the manufacture of boric acid and sodium sulphate, the improvementwhich comprises parafter separation of boric acid and before separationof sodium sulphate to prevent loss of boric acid with the separatedsodium sulphate.

10. -A process of manufacturing boric acid and sodium sulphate, whichcomprises treating a soluing solution, treating the solution with'asodium containing compound capable of increasing the solubility of boricacid and partially crystallizing out sodium sulphate from the solution.

11. A process of manufacturing boric acid and sodium sulphate, whichcomprises treating a solution including sodium tetraborate withsulphuric acid to form boric acid and sodium sulphate, partiallycrystallizing out boric acid from the resulting solution, treating thesolution with a sodium containing'compound capable of increasing thesolubility of boric acid, and partially crystallizing out sodiumsulphate from the solution, and returning the solution remaining'afterthe latter separating operation to the first treating operation.

12. A process of manufacturing boric acid and sodium sulphate whichcomprises treating a solution including a sodium borate with sulphuricacid to formboric acid and sodium sulphate, cooling the solution topartially precipitate boric acid, then treating the solution With asodium compound capable of increasing the solubility of boric acid, andcooling the solution to partially precipitate sodium sulphate.

13. A process of manufacturing boric acid and sodium sulphate whichcomprises treating a solution including a sodium borate with sulphuricacid to form boric acid and sodium sulphate, cooling the solution topartially precipitate boric acid, then treating the solution with asodium compound capable of increasing the solubility of boric acid, andcooling the solution to partially precipitate sodium sulphate,and'treating the remaining solution and additional sodiumborate withfurther sulphuric acidr 14. In the process of manufacture of boric acidand sodium sulphate, the steps comprising treating a sodium containingborate material with sulphuric acid in amounts sufficient to form asolution nearly saturated with pentaborate, filtering the solution, thentreating the solution with additional sulphuric acid necessary to formboric acid, cooling the solution to partially precipitate the boricacid, then treating the solution with a sodium compound capable ofconverting the remaining acid to the pentaborate, and cooling thesolution topartially precipitate soluble sulphates. g 15. A process ofmanufacturing boric acid and sodium sulphate which comprises bringing asodium borate material into solution in the presence 'of sulphuricacid'to produce boric acid, cooling the solution to partiallyprecipitate boric acid therefrom and separating said boric acid from thesolution, then treating the solution with sodium compound capable ofincreasing the solubility of boric acid, cooling the solution topartially precipitate sodium sulphate, separating the sodium sulphatefrom the solution, and recycling the solution to the first operation.

16. A process of manufacturing boric acid and a by-product salt, whichcomprises treating a solution containing sodium borate with a mineralacid to form boric acid and a by-product salt, partially crystallizingout boric acid from the resulting solution, treating the solution with asodium containing compound capable of increasing the "solubility ofboric acid and partially crystallizing out said. Icy-product salt fromthe solution.

17. A process of producing boric acid'and sodium sulphate, whichcomprises treating a solution including a sodium borate with sulphuricacid to form boric acid and sodium sulphate, partially crystallizing outboric acid from the resulting solution, treating the solution with asodium c oniio taining compound capable of increasing thesolubility ofbcEcnaciel an d partially crystallizing out sodium sulphate from thesolution. 7

v 18. In 'a process of treating solutions containing boric acid and asalt of a strong mineral acid, the steps comprising adding a sodiumcontaining compound capable of increasing the solubility of boric acidand partially crystallizing out said salt from solution. 19. The methodof separating sodium sulphate from boric acid Which comprises treating asolution containing sodium sulphate and boric acid with a sodiumcontaining compound capable of increasing the solubility of the boricacid, and crystallizing sodium sulphate from the solution. WILLIAM E.BURKE.

HARALD DE ROPP.

